Maybe he is paralyzed from the neck down, so he has to control everything with his mouth: his wheelchair, his computer, his phone, etc. As a result, he develops extreme strength and dexterity with his lips and tongue. Naturally, that makes him extremely good at cunnilingus......

Two brothers are equally damaged in a terrible auto wreck that broke nearly every bone in their bodies. Critical surgery;l then they're placed in a state-of-the-art physical rehab facility. Till their bones set, they're immobilized in adjacent beds (private room) that are power-mounted for full-360 mobility -- can take almost any position. This reduces chance of clotting and bed sores.

One nurse spends much assigned time with the brothers. She soon accedes to their sexual needs, blowing them sequentially. In time, the brothers argue about who should be blown first and best. The nurse eventually tires of their squabbling and positions the beds so the brothers can blow each other. Hilarity ensues.

Two brothers are equally damaged in a terrible auto wreck that broke nearly every bone in their bodies. Critical surgery;l then they're placed in a state-of-the-art physical rehab facility. Till their bones set, they're immobilized in adjacent beds (private room) that are power-mounted for full-360 mobility -- can take almost any position. This reduces chance of clotting and bed sores.

One nurse spends much assigned time with the brothers. She soon accedes to their sexual needs, blowing them sequentially. In time, the brothers argue about who should be blown first and best. The nurse eventually tires of their squabbling and positions the beds so the brothers can blow each other. Hilarity ensues.

Another person that could fall (mutually, even) for a disabled man would be a physical therapist. All that time spent cheering him on, helping him stretch, etc. could lead to getting to know him and him getting to know her. It might not even dawn on them the sexual tension that is building between them until he finishes whatever run of PT he was authorized by his doc.

I would start off with this disabled guy, perhaps in a wheelchair, seeing her through the window at her house getting it on, perhaps more than once, so he has more of an idea that she is interested in casual sex. Then he could put it to her in conversation that she knows she has casual sex. He could describe what he saw and how hot she looked. She could get excited by his retelling of these escapades, and that could turn them both on.
Her visits could become regular when one of the parents needs dialysis or some other regular treatment and the other must drive.
Then their relationship could build and after a while, he could propose.
Not much kink to the story, but it's an idea.